This invention relates generally to vitrectomy control systems for vitrectomy probes.
The eye is divided into two sections, the anterior section and the posterior section. The anterior section contains the cornea, iris, anterior chamber, ciliary body and lens. The posterior section contains the vitreous, retina, choroid and sclera. Certain ophthalmic surgical procedures require the incision and removal of all or part of the vitreous in the eye. This procedure is known as vitrectomy and surgical instruments commonly known as vitrectomy probes have been developed for this purpose.
Vitrectomy probes typically comprise a stationary outer needle which contains one or more apertures to receive the vitreous when suction is applied. A cutting blade located within the outer needle cuts the fibers of the vitreous as it is drawn into the needle. The cutting blade of the vitrectomy probe is typically driven via pneumatic or electrical pulses generated from a pneumatic or electrical source, respectively. The interval between pulses (i.e., period) defines the cut rate of the cutting blade of the vitrectomy probe. The duration of each pulse and the pulse period in turn define the drive characteristics of the vitrectomy probe.
Different surgical techniques require different drive characteristics. Accordingly, a variety of different types of vitrectomy probes having different drive characteristics have been developed. The structure of the various areas of the posterior section of the eye are also significantly different. Some areas, such as the retina, are more sensitive than other areas. Moreover, the structure of the eye itself is different from individual to individual. Therefore, a specific concern in the use of vitrectomy probes is the ability to accurately, reliably and automatically control its drive characteristics on demand in order to accommodate all of these various differences.
Existing vitrectomy control systems use pneumatic delay valves, monostable multivibrators, external microprocessor peripheral timing chips or external programmable, logic-based counters to control the drive characteristics of vitrectomy probes. However, because of limitations in complexity due to both cost and hardware constraints, the parameters for the pulse duration which in part defines the drive characteristics of the vitrectomy probe are set by loading pre-selected timing values into the external peripheral chips, discrete counters or programmable logic. Any changes in these pulse duration parameters require a significant hardware redesign. Moreover, these changes typically cannot be implemented by a surgeon or nurse, but rather require a trained technician. The above-mentioned hardware constraints of existing vitrectomy control systems therefore severely limit the types and number of vitrectomy probes that can be supported by any given system.
The above-mentioned limitations not only affect the functional or performance aspects of a vitrectomy probe, but also have a significant affect on its reliability and safety. The timing mechanisms implemented by existing vitrectomy control systems require several integrated circuits and interconnections. Each additional circuit and each additional interconnection, however, increases the risk of failures and defects and thus, decreases the reliability and safety of the probe. In some cases, such failures and defects can cause serious injury to the eye. The complexity of the hardware also increases the overall cost of the vitrectomy control system.
Accordingly, a need has arisen for a vitrectomy control system for accurately, reliably and automatically controlling the drive characteristics of a vitrectomy probe on demand by a user over a wide range of pulse durations and cut rates.